This application is related to International Application No. PCT/FR98/00984, filed May 15, 1998, the entire specification of which is incorporated herewith by reference.
This invention concerns the orthodontic or dento-facial orthopedic apparatus sector, particularly those which are precisely adapted to the specific morphology of each patient.
More particularly, it concerns all orthodontic or dento-facial orthopedic apparatuses having a general hollow body which may have one or more openings, variable thickness, and which, due to this particular geometry, cannot be produced from a flat plate.
Such apparatuses, which may be removable, may be those intended to maintain a patient""s tongue in a given volume, particularly Bonnet""s Nighttime Lingual Envelope or N.L.E.
More generally, the invention concerns apparatuses which must necessarily be adapted very precisely to each patient or user in order to fulfill their function and which cannot be manufactured based on a blank in the form of a flat plate due to their final complex shape (open hollow body, variable thicknesses which cannot be obtained by simply shaping a plate, etc.). By contrast, these apparatuses are produced starting from a blank or preform whose shape permits it to be expanded in a mold that reproduces the patient""s morphology. This preform has the general shape of a three dimensional hollow body, more particularly, a hollow, tubular or approximately tubular form, more particularly still, a hollow, tubular or approximately tubular form which is cut on the upper anterior part to form an opening.
Traditionally, such apparatuses are tailor-made, created in a laboratory and therefore, piecemeal, starting from formed molds based on research models which have themselves been formed based on an impression or impressions made in the practitioners office by the same.
Several apparatuses are generally necessary during treatment, to follow changes in the patient""s morphology. The need to produce a new apparatus during treatment may also come from the need to move the fastening hooks due to a change in the environment (for example, with the appearance of wisdom teeth or with shifting of teeth). Each time a cast must be taken to produce a model, then a mold, and then the final apparatus must be produced.
More specifically, the traditional process for manufacture is a contact molding process. It occurs in four steps:
Construction of the Mold
The practitioner makes a casting of the upper maxilla and possibly a casting of the lower maxilla of his patient, most often with alginates due to their rapid polymerization and biocompatibility properties. These castings act as a base for the production of a model in one or two parts which is most often in plaster, completed using wax that sticks easily and/or is easily deformed. This requires that the technician have great technical proficiency, integrating brief perceptions, dexterity, and experience. The technician, also using wax, positions the fastening systems (or fastening hooks and pins), generally metal wires which shall then be duplicate molded and shall perform the fastening function of the completed apparatus in the patient""s mouth as well as any other additional necessary piece.
Contact Molding
A resin with two components is used, a solid powder and a fluid, adapted to contact molding of traditional orthodontic pieces. Work is conducted with successive passes of dampening by the liquid using a pipette and/or dusting with the solid.
However, the shape of the hollow body with variable thickness in certain apparatuses such as the N.L.E. by Bonnet results in special difficulties during production since the different areas of the apparatus have quite varied orientations and curvature radii. Therefore, the technician is confronted with several difficulties.
(i) A compromise must be found between passes that are too liquid or too thin or of such small surface that multiples are needed, thus lengthening the operating time, and passes which are too thick or too pasty which creates irregular upper thicknesses that will then need grinding.
(ii) It is difficult to estimate or measure the deposited thicknesses to inspect ones work as it progresses,
(iii) A choice must be made between molding of all passes in a single operation lasting several minutes or up to a quarter of an hour followed by a single final polymerization or molding with several very brief operations each lasting approximately a minute with as many intermediate polymerization phases in an autoclave pressurized above atmospheric pressure (otherwise gas bubbles arise deterring from the piece""s final appearance). In the first case, one obtains a piece having irregular transparency and which is little flattering, in the second case, the production time, and therefore the cost are noticeably higher.
Mold Ejection and Finishing
The blank is ejected from the mold, then finishing takes place using machining and grinding. The shape of the preform being somewhat removed from the final piece, finishing is a long and delicate operation generating noise and dust. Since this pollution is incompatible with a dentist""s office, finishing must take place in an area with specific equipment, namely, for example, a suction hood.
There are variations in which the teeth and gums part of the lower maxilla model are used complementing the upper maxilla model. A filler material (for example, plaster) is used to complete the missing part in order to obtain a complete mold. In this case, the mold is completely exterior to the piece to be molded; the general accessibility and visibility are not as poor as in the preceding variation.
The apparatus is then equipped with hooks in order to be attached to the patient""s mouth. Currently, there are mainly two types of hooks or claws or fastening systems, hereafter fastening hooks, (Step 1) used depending on the morphology and the dental age of the patient, in general made of stainless steel orthodontic wires:
Lateral Hooks (Generally Symmetrical, Totaling 2)
They are used especially for young children. They are anchored in the apparatus at one end which is inserted in the lateral wall of the apparatus, the other end being inserted elastically into a diastema to attach the apparatus to the mouth. They are generally cold-formed using the Sahar method, meaning that the beginning of the emerged part has a zigzag shape such that it may be deformed by the practitioner to adjust the tightness of the anchoring when it is first placed in the mouth and on the following visits depending on the changes in the patient""s oral environment, all without changing the anchoring, that is, the position of the part of the hook included in the apparatus. In the thickness of the outside wall of the apparatus, a hollow is reserved to lodge this zigzag whose shape changes during the apparatus"" life.
The Posterior Hooks (Generally Symmetrical, Totaling 2)
They are anchored in the apparatus such that the wire exits at the rear of the apparatus approximately in the horizontal occlusion plane. The wire then generally follows the contours of the teeth which are farthest back (for example, the 6 year tooth or the 12 year tooth), then it comes to exert pressure from the outside on the tube of a ring. It is formed in such a way that with the slight symmetrical forces of the two posterior right and left hooks pressing upward and outward in reaction to the apparatus it is kept in position against the palate.
This production method offers certain inconveniences. In effect, production costs are high (made to order), the appearance and quality of the product are often insufficient (manual), at times, considerable finishing is needed, delays are excessive. Furthermore, the alginate cast is destroyed when the plaster model is released from the mold. Therefore, the model must not be damaged so that the patient does not have to undergo the procedure again. So, this plaster model is very fragile. It must be handled all the more delicately, which requires more care and time. Finally, the procedure generates noise, dust, and odors (solvents, etc.).
Attempts at thermoforming have been made in order to be freed from some of the disadvantages linked to the traditional procedure. The thermoforming technique is widely used for producing orthodontic apparatuses and is described in many general works.
In the domain of orthodontics, the document DE 36 10 349 may be mentioned. It describes a process and mechanism to create an orthodontic apparatus. The base material is present in the form of a plastic film with constant thickness, maintained by film supports which undergo deformation through the addition of heat and applied pressure, until a model is created based on casting taken directly from the patient.
Michel AMORIC""s publication: xe2x80x9cGouttieres orthodontiques et orthopxc3xa9diques thermoformxc3xa9esxe2x80x9d Thermoformed orthodontic and orthopedic splints, 1993, Editions SID can also be mentioned. The principle behind this technique is that one uses a flat plate as a base material with a constant thickness. Starting with a traditionally produced mold the plate is deformed so as to obtain an apparatus having an appropriate shape.
Not all apparatuses can be obtained by this method. In particular, this method is not efficient for apparatuses having a hollow body and variable thickness. The stretching that the plate must withstand in these specific cases is considerable and therefore difficult to obtain without tearing. Most of all, thicknesses cannot be controlled since they are simply dependent on the stretching necessary to obtain the desired shape and are therefore irregular since not all areas are stretched in the same manner. This technique is therefore not appropriate for a certain number of cases.
The variant consisting in the use of a two part apparatus, that is, two base plates yielding two half-apparatuses that are assembled is also not adequate. It allows a decrease in the stretching undergone by the plates, and therefore in the risks of ripping and the problems of too irregular thicknesses, but the problem is in part displaced to the assembly of the two half-apparatuses obtained. In effect, the difficulty lies in the precision and solidity of the glued or soldered assembly, inasmuch as one must also install in this assembly area the fastening hooks for the fastening of the apparatus in the patient""s mouth.
The thermoforming methods used up to present day therefore do not allow the production of apparatuses with hollow bodies and variable thicknesses and the risks of damaging the sole plaster mold are significant.
The invention allows these problems to be solved by proposing a three dimensional apparatus that can be produced in series, thereby at low cost; this apparatus is called a preform. This preform is different from a flat plate and has a general shape permitting it to expand in a mold that reproduces the patient""s morphology. This preform has the general shape of a three-dimensional hollow body, more particularly, a hollow, tubular or approximately tubular form, more particularly still, a hollow, tubular or approximately tubular form which is cut on the upper anterior part to form an opening. Said preform may then be perfectly adapted to each patient in the practitioner""s office or in the prosthesis maker""s laboratory by a deformation process including expansion that is quick and easy to implement, in a mold constructed starting with a plaster model, without any risk for said plaster model. It allows a functional apparatus to be obtained which cannot be obtained by traditional thermoforming starting with a flat plate.
The term xe2x80x9ctechnicianxe2x80x9d shall refer to the person transforming the preform into a functional apparatus, whether this is the practitioner in the office or the prosthesis maker in the laboratory.
More specifically, this preform is manufactured in a biocompatible material due to the at times prolonged contact with a human cavity [the mouth]. It must, in this respect, meet current applicable standards. It may be a thermosetting or thermoplastic type of plastic material deformable through expansion and obtained, for example, by injection or any other appropriate industrial process (first stage processing), and presenting a three dimensional shape such that its deformation easily allows for the creation of the final apparatus adapted to each patient. This deformation or second stage processing, which includes expansion, is performed rapidly and easily by the technician according to the patient""s morphology.
In this description, expansion of the preform means the volumetric development or deformation of the preform.
The invention has merit in that it has removed the disadvantages related to the necessary production and individualized adaptation of an orthodontic apparatus by permitting low-cost series manufacturing of a preform which shall then be easily adaptable to the patient by the practitioner or prosthesis maker in order to obtain, after finishing, a functional apparatus with a hollow body of varying thicknesses that would not be possible with the simple deformation of a flat plate, and, in some variants (particularly if thermoplastic material is used) is capable of being equipped with fastening hooks in the mouth by a process which allows changes in anchoring points.
The production cost is therefore lower; the delays are shorter; the process is clean (without dust, noise, or odor) and simple to implement, without risk to the plaster model, and facilitates the technician""s work.
The shape of the preform is defined while taking into account mean deformations to which it shall be subject during second stage processingxe2x80x94for example, reduction of thickness and width variables of the walls, according to the desired functional apparatus. It is therefore possible to envisage a preform for such an apparatus and for patients of a given size or gender or age. Thus, series production of the preform is allowed even while limiting the deformations that it shall undergo, thereby the lengths and complexity of the second stage processing.
In one variation, it is also possible to imagine having the preform manufactured and delivered to the technician in a developed flattened shape, thus generally shaped in two dimensions and no longer in three dimensions. This is called a developed preform. Such a case shall be detailed later making reference to figures. The developed preform is then given a volume by the technician by rolling or bending around an appropriate gauge which may be a controlled expansion core to create the preform as such. Thus, the production cost is decreased, as is the volume of the preform manufactured in series which, here, is a developed preform. Furthermore, this structure in two dimensions facilitates certain manipulations by the technicians (preparation of an opening, etc.). However, the possibility to define the thickness at each point of the preform is retained since the developed preform may itself be of a variable thickness according to each area. The connection (cross-section) to recreate the hollow body is located in the least deformed area during expansion, for example the bow of a slide in the case of Bonnet""s N.L.E. The weld is performed by hand using pressure (for example, a self-adhesive effect, by application of a solvent or glue adapted to the material of the developed preform) such that it then resists expansion.
The second stage process is dependent on the plastic material used. If thermoplastic plastic materials are used, the second stage process may be carried out with techniques belonging to blowing, thermoforming, injection blow molding, even mechanical means or any other appropriate means. If thermosetting material is used, the second stage process may be carried out with techniques similar to compression, dry bag molding, vacuum molding, preforming on a diaphragm, or any other appropriate means.
This second stage process shall be performed by the technician, that is to say, by the practitioner, in his office or by the prosthesis maker in his laboratory, rapidly and easily by a xe2x80x9ccleanxe2x80x9d process, that is to say, without dust, noise or odor, within very short time frames and in conditions that allow perfect adaptation to the patient""s morphology.
Furthermore, the different apparatuses necessary during treatment due to changes in the patient""s morphology can be produced successively based on the first apparatus produced from a preform. Thus, the first apparatus shall become the preform for the second apparatus which shall be necessary some months later, this second apparatus becoming in turn, the preform for the third, etc. The transformations shall therefore be rapid since it is not necessary to start from scratch each time, unlike present day practices.
The process of the invention also allows the anchoring position of the fastening hooks to be moved slighting in the apparatus at the time of installation in the mouth and/or during treatment, thus, in some cases, avoiding the manufacture of a new apparatus.
Other characteristics and advantages of the invention shall be better understood by reading the description which follows, referring to the included figures in which: